Conventional gasoline engines operate at a fixed compression ratio, which is set low enough to prevent premature ignition of the fuel, or “knock,” at high power levels under fast acceleration, high speeds, or heavy loads and thus. However, most of the time gasoline engines operate at relatively low power levels under slow acceleration, lower speed, or light loads. If the compression ratio were increased at low-power operation, gasoline engines could achieve higher fuel efficiency.
In the last 100 years a multitude of engines with variable compression ratio (VCR) systems or VCR mechanisms have been proposed and designed to control and vary the volume of the combustion chamber of a cylinder in order to achieve improved fuel economy and increased engine power performance. Such VCR engines are designed to have a higher compression ratio during low load conditions, and a lower compression ratio during high load conditions. Known techniques include using “sub-chambers” and “sub-pistons” to vary the volume of a cylinder (see, for example, U.S. Pat. Nos. 8,166,929 and 8,136,489), varying the actual dimensions of all or a portion of a piston attached to a fixed length connecting rod (see U.S. Pat. No. 8,166,928), and use of eccentric rings or bushings either at the lower “large” end of a connecting rod or the upper “small” end of the connecting rod for varying the effective length of the connecting rod (see U.S. Pat. Nos. 5,562,068, 5,960,750 and 6,202,622).
Other techniques include use of different VCR mechanisms as well as use of eccentric rings or bushings to change position of a crankshaft of the engine in order to change positions of the top dead centre (TDC) and the bottom dead centre (BDC) and thus to vary the volume of the combustion chamber of the cylinder (see U.S. Pat. Nos. 6,202,623, 6,588,384 and 7,174,865).
The foregoing art, however, have weaknesses such as considerably increasing overall complexity of an engine which results in increased cost of manufacturing and maintenance, as well as increased response time for change in compression ratio or a restricted a range of compression ratio and often with added friction loses as well.